A support means fastening is usually arranged at a fixed structure (building part or brackets or similar supported at the guide rails) in that a support means end connection is held by a tie bar or tie rod supported at the fixed structure. A compression spring, which serves as length compensation for the support means, can be provided as support.
The support means end connection is, for example, a connection functioning on the wedge principle and can be a part of a stationary support means fastening or a part of a support means fastening arranged at the elevator car and/or part of a support means fastening arranged at a counterweight. The former is usually the case with a 2:1 cable guidance and the latter, for example, in the case of a 1:1 cable guidance.
In both 2:1 and 1:1 forms of cable guidance or, however, also in the case of forms of cable guidance in furtherance of the principle it can happen depending on the respective size of the elevator installation or arrangement of guide rails, drive pulley, elevator car or counterweight that the support means when describing the maximum travel of the elevator car or the counterweight from the deepest shaft position to the highest shaft position is deflected from the perpendicular or the vertical. It is also possible for an oblique guidance of the support means to be realized from the outset, for example because in the case of the so-termed rucksack suspension it is desired to utilize the horizontal force components of the oblique support means guidance as a force attracting the elevator car or the counterweight to the guide rails.
The deflection of the support means away from the perpendicular or the vertical, which fundamentally occurs with all forms of all suspension in which the support means fastenings, the outer diameter of the support rollers and the outer diameter of the drive pulley are not vertically aligned relative to one another, has the consequence that the support means at the support means end connection and the tie rod are buckled to greater or lesser extent during operation of the elevator installation depending on the height position of the elevator car or the counterweight.
This buckling stress in turn can over time represent an undesired loading or material fatiguing for the support means, which leads to a premature exchange of the support means, but at least to a requirement for checking and maintenance, or even to fracture of the support means.
In general, for avoidance of horizontally arising forces which manifest themselves as bending or shearing forces in a tie rod, pairs of washers are known in which a convexly formed side of one washer fits in a correspondingly concavely formed side of the other washer. However, it is disadvantageous with such solutions that the pivotability is limited to only a small deflection angle and is subject to high friction forces.
Fundamentally, in such solutions the undesired horizontally arising forces are, in fact, no longer accepted solely by the material of the tie rod or its bending resistance, but compensation is simply provided by the friction forces. The overall situation of the arising forces in the relationship thereof to one another is thus not satisfactorily solved. Lateral, i.e. horizontally acting, force components continue to arise. Co-pivotation or adaptation, which is as free as possible, to the deflection angle with simultaneous full transmission of the vertical holding force is thus not achieved.
Due to the high friction forces it can be observed in these solutions that only a dynamic adaptation takes place, i.e. when the elevator car or the counterweight moves during operation or the deflection angle just changes then the convex/concave washers adapt to the deflection. By contrast, in the static case, i.e. when the elevator car or the counterweight is stationary, due to the high level of friction between the convex and the concave surface of the washers no adaptation takes place.
Consequently, the smallest possible friction is ensured at this location in that lubricants are used and/or the surfaces are treated or special low-friction and self-lubricating synthetic materials are used. This in turn makes the solutions complicated and cost-intensive, although ultimately in terms of mechanical basic principle they always represent only a compromise.
Patent specification U.S. Pat. No. 6,341,669 B1 discloses, for avoidance of buckling stress and for producing a constant deflection angle of the support means at the two sides of the elevator car, a stationary, but pivotable support means fastening which is identical in terms of mechanical basic principle. A hemisphere or a shank in the form of a longitudinally bisected cylinder is in that case arranged in a correspondingly concavely shaped seat. This seat, in order to keep the friction as small as possible, is preferably made from a technical synthetic material, namely acetal plastics material of the company Dupont under the name Delrin (Registered Trade Mark).